Looks like Septoria leaf spot to me. Removing infected leaves and spraying with a fungicide like Daconil, Copper soap, Seranade can help slow it down enough to harvest the tomatoes that are already on the plant.

Mulching the soil under the plants well can help prevent the soil from splashing up on the leaves and spreading the fungus. Pruning the lower 12-18" of branches off the plants as they grow is also a good practice for prevention. Preventative fungicide spraying before symptoms appear is a common practice as well.

Agree with the Septoria diagnosis. "Saving" the plants is likely too late. Once the disease is that advanced it is already systemic. But good fungicide treatments now might let them hang on until current fruit ripens as Jack said above.

Next year plan to get a much earlier start on fungicide applications.

Dave

Wow, I have been growing in this spot for about 10 years (alternating tomato years) and have never had this happen. I'm assuming all 4 plants in this bed will be affected?

Anything that I can start now that will not be affected by septoria and still mature before winter?

DO NOT compost the foliage. Dispose of it securely. I'm not a big fan of crop rotation, but in this case, you might not grow tomatoes there for a year or two. That being said, there are new cultivars that are alleged to be SLS resistant. That's "resistant". Not "immune".

Hi there! I was (am) having this problem too. It was so rainy this spring! A few items of note.

1) I gave mine a good haircut, got rid of any leaders without fruit on them and all the leaves with spots, and sprayed with both copper and daconil. They looked pathetic but they are growing laterals now that look "clean." Maybe it's systemic but maybe I can stave it off. When the fruit ripens (and a lot of it already has), I'm going to top them off and see what happens with all those new low laterals.

2) Someone on my question thread from a few weeks ago suggested that I grow some determinates. They usually take about 50-60 days to throw fruit. I found a few determinate varieties on the sale tables around town and have potted out into gallon containers until some of the others die. :) I also started a few determinate seeds inside just to see what happens. Last year, I was harvesting tomatoes well into October. So the price of a few seeds and maybe some frostbitten plants I will sacrifice for science and optimism. ;)

3) Most of mine (14 out of 20) are in containers on my back patio because of a hefty deer population. The ones on the side of the house in the ground are doing pretty well and so far the deer have left them alone. But at any rate, the same person who suggested the determinates, also suggested keeping them in a spot where they get morning sun, and that applies to my in-ground plants. The morning sun dries off the dew before it has a chance to do any more damage. My patio is west facing which leaves everything in darkness until noon.

4) Don't have "a moment" and rip everything out. They'll hang on. Trim, water, feed, treat, repeat. :) I harvested about 6 tomatoes yesterday, and it's my second pass, and there are about 12 turning the corner to be picked by the end of the week. I posted my question 6/26 so it's been three weeks and they're still doing their thing.

5) There's always next year! I forgot to go through my usual routine of pouring some hydrogen peroxide over the top of the potting soil (kills mold spores) in the big pots before potting out. And I should have done a preventative copper spray and I also forgot that. People forget. Life is hectic. Spring is always busy. Don't kick yourself too much.

Good luck!